The bolt for the valve cover snapped off, does anyone know a good drillbit that can pierce ARP bolts? I tried using a cobalt bit with no luck.

You may be able to use a small punch and a hammer to slowly rotate the bolt. I did this once on a cam bolt i broke off.

Hope this helps.

or a left handed drill bit(drills in reverse) as it starts to drill into the bolt it catches and screws the bolt out